States / South Dakota
60 counties · median score 23
Crawl space moisture in South Dakota
Most of South Dakota drains well: only 0 of 60 counties score high or elevated, and the median is 23. Clay County is the exception at 37; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Clay County
- 2High or elevated 0 of 60
- 3Median score 23
- 4Driest county Lawrence County
South Dakota's soil, taken as a whole
Across the 44,773,471 acres mapped in these 60 counties, 9% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 30% of acres report a seasonal water table within about two metres. That is a dry figure; wet soils here are confined to river bottoms and wetlands. 60 of the 60 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 2.5% |
| Somewhat excessively drained | 1.9% |
| Well drained | 78.8% |
| Moderately well drained | 8.2% |
| Somewhat poorly drained | 3.1% |
| Poorly drained | 3.7% |
| Very poorly drained | 1.8% |
Radon. By EPA zone, 44 South Dakota counties here are zone 1 (highest potential), 15 zone 2 and 0 zone 3; 1 are not in the EPA table. With most of the state in zone 1, any crawl-space sealing project here should start with a radon test and be designed to take a radon fan.
Every South Dakota county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the South Dakota numbers
The wettest county, Clay County, is 57% well drained by dominant condition, with a seasonal water table averaging 2.2 ft below grade across the 91% of acres that report one, and sits in EPA radon zone 1. The driest, Lawrence County, is 97% well drained. No South Dakota county reaches the high tier.
The score is a guide to the soil, not to a house: a well-graded lot with working gutters in a high county can have a dry crawl space, and a bad downspout can flood one in a low county. The R408 calculator sizes venting or encapsulation for any footprint.
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted; EPA Map of Radon Zones, county table (June 2024 JSON). Checked 2026-10-23.